1. Field of the Invention
The present invention relates to tanks for storing gas in a road vehicle whatever its motorization, and more particularly but not solely applicable for the storage of gaseous hydrogen and/or the storage of gaseous oxygen in a vehicle with a fuel cell.
2. Description of Related Art
One of the problems posed by the storage of gas on a vehicle is the danger of fire occurring in the vicinity of the tank and of the pressure rising too highly. Discharge valves have already been proposed for liquefied petroleum gas vehicles in order to allow the gas to escape progressively in case of excess pressure caused, for example, by abnormal heating due to a fire. Because it is necessary, at all costs, to avoid the risk of explosion, even if it means that the fuel feeds a fire below a limited output. This is why safety valves which are opened irreversibly under the effect of overheating have already been proposed in the state of the art. For example, patent application JP60/073200 which describes such a safety valve in which the sealing element is a membrane sealing an orifice and the element controlling a definitive opening is a pellet produced in a shape memory alloy carrying a needle so that, in case of overheating, the pellet made of a shape memory alloy changes shape and pushes the needle back against the membrane until rupture of the membrane occurs.
However, no solution is known which is sufficiently robust to be installed in a car and for playing a safety role solely in case of fire. Hence, for example, no satisfactory solution is known to make it possible to avoid gaseous fuel that escapes from the tank aggravating a fire which might have occurred without the fuel supply system being the root cause. Hence, in case of an accident involving several vehicles, if one of these vehicles loses its fuel which then spreads over the road, there is a significant risk that the fuel will catch fire and that another vehicle will find itself immobilized above this fire. In this case, if the fire takes place under the gaseous fuel tank of this other vehicle, supposing that the latter is equipped with a discharge valve in case of excess pressure, it is necessary first of all to wait until the pressure in the tank rises before such a safety element plays its part. Furthermore, if the pressure prevailing in the tank is low because the residual quantity of fuel is low, it will be necessary to wait longer before such a security element acts, at such a point that the material forming the tank might have lost its mechanical properties to the point of yielding and therefore provoking an explosion before even the pressure is sufficiently raised for the discharge valve to act in case of excess pressure.
If one were able to act sooner to vent the tank, the safety conditions of the vehicles storing a gaseous fuel under pressure would improve, in particular in vehicles with a fuel cell which function on hydrogen.
In the field of fuel cell vehicles, patent application WO03/035419 proposes means for evacuating hydrogen not consumed by the cell, by collecting the leakages around the cell and the tank, and by installing an excess pressure valve on the tank. Here again, nothing is provided to improve safety in case of fire.